Electrostatic coating apparatus with automatic self-wiping means



Feb. 2, 1960 R. J. EMMERT 2,923,272

ELECTROSTATIC comma APPARATUS WITH AUTOMATIC SELF-WIPING MEANS FiledNov. s, 1955 4 Sheets-Sheet 1 IN VENTOR.

xx BY j/ZZQ/Q AT TORNEV Feb. 2, 1960 R. J. EMMERT 7 2,923,272

ELECTROSTATIC COATING APPARATUS WITH AUTOMATIC SELF--WIPING MEANS FiledNov. 3, 1955 4 Sheets-Sheet 2 I INVENTQR acffmr zerf ATTORNEY Feb. 2,1960 R. J. EMMERT 2,923,272

ELECTROSTATIC COATING APPARATUS WITH AUTOMATIC SELF-WIPING MEANS FiledNov. 3, 1955 4 Sheets-Sheet 3 I #61. M7 Q I aVfNfQ R 5; fi t/5W; 307/ A!5 ATTORNEY A Feb. 2, 1960 R. J. EMMERT 2,923,272

ELECTROSTATIC COATING APPARATUS WITH AUTOMATIC SELF-WIPING MEANS FiledNov. 3, 1955 4 Sheets-Sheet 4 L? @5 200 w $52 465 i TIME/e 65 /2 swearsINVENTOR.

supp" ATTORNEY United Sates Patent Of ELECTROSTATIC COATING APPARATUSWITH AUTOMATIC SELF-WIPING MEANS Rodger J. Emmert, Birmingham, Mich.,assignor to General Motors Corporation, Detroit, Mich., of DelawareApplication November 3, 1955, Serial No. 544,763 8 Claims. (Cl. 118- 4)This invention relates to improvements in electrostatic coatingapparatus and to electrostatic atomizing devices therefor. Morespecifically, the invention is concerned with atomizing devices of thetype in which paint or other liquid coating material is supplied at acontrolled rate to the discharge orifice of an applicator device and iscaused to flow and to be atomized therefrom by the cataphoric action ofa high potential electrostatic field established between the applicatorand an oppositely charged article to be coated.

Such electrostatic atomizing devices as have been proposed heretoforehave proven to be impractical owing mainly to the clogging by paint,dirt and other particles of the very fine discharge orifice required toobtain atomization and to the difficulty of obtaining a satisfactoryspray and article deposition pattern therefrom.

The present invention has among its general objects to provideimprovements in electrostatic atomizing devices and coating apparatus ofthis character from the standpoint of facilitating their adjustment andcleaning, promoting uniformity of paint flow and improving the spray andarticle deposition pattern therefrom. Related objects are to improve theoperating efliciency and to reduce the paint consumption ofelectrostatic coating apparatus of this character.

In the drawings:

"Fig. l is a cross-sectional, longitudinal view of a form of applicatordevice in accordance with the present invention;

Fig. 1A is a cross-sectional, longitudinal view of the applicator ofFig. 1 equipped with a drive mechanism for rotating a part thereof;

Fig. 2 is an enlarged cross-sectional view with parts broken awayshowing a modified part of the apparatus of Figs. 1 and 1A;

Fig. 3 is a diagrammatic illustration of a related form of applicator inaccordance with another embodiment of the present invention;

Fig. 4 is a front view of another form of applicator in accordance withthe present invention;

Fig. 4A is a modified form of the applicator of Fig. 4;

Fig. 5 is a cross-sectional, longitudinal view taken in the direction5-5 of Fig. 4;

Fig. 5A is a cross-sectional view of a part shown in Fig. 5;

Fig. 6 is anenlarged, fragmentary portion of Fig. 4;

Fig. 7 is across-sectional, fragmentary view taken in the direction 7-7of Fig. 6;

Fig. 8 is a view taken in the direction 88 of Fig. 5;

and

Fig. 9 is a diagrammatic illustration of an electrostatic spray paintinginstallation and an electrical control system for a form. of applicatorused therein in accordance with the present invention.

Referring to the drawings, Fig. 1 illustrates a form of applicator heador gun in which paint. or other liquid coating or film forming materialmay be finely atomized without the use of compressed air. The applicator10 a corporation 2,923,272 Patented Feb. 2, 1960 comprises a generallyspherical, outer body member 11 and a spool-shaped or piston-like innermember 12, which is received within a deep cylindrical'cavity 14 formedwithin the body member. The forward portion of the wall of the cavityforms 'with the outer surface of the body member a continuous lip 16which is extended in a direction generally parallel to the axis of theapplicator. The lip 16 may be of circular, or approximately circular,shape and has a thin discharge edge 18 which may be of knife-likesharpness.

The inner member has a threaded central stem or rod portion 22, which iscoaxially received in a threaded body opening 24 that extends into thebody cavity. The forward portion of the inner member is shaped toprovide a continuous and substantially circular lip 26 also terminatingin a thin knife-like discharge edge 28.

The discharge edge 28 of the inner member is spaced slightly from theouter member and forms therewith an annular opening or discharge orifice30 for an annular passage 32, the curved walls of which are held toclose limits of concentricity in order to obtain uniform flow of paintthroughout the entire circumferentialclearance space between the outerand inner members forming the passage. The passage 32 communicates atits inner end with an annulus 34 formed by an annular groove in eitherthe inner member or outer member or by a pair of annular grooves in theadjacent curved'surfaces of the outer member and the inner member, asshown. Paint or other liquid material is supplied under some pressureand at a uniform delivery rate to the annulus 34 from an external liquidsupply line 35 (Fig. 9), which is suitably connected to the body memberand communicates with an obliquely extending supply passage 38 leadingto the annulus. An O-ring or other seal 40 located behind the annulus isprovided in an annular groove in the inner member to prevent fluidleakage into the interior of the-applicator.

The outer end of the stem 22 of the inner member may be slotted,'orotherwise formed, as shown at 42, to receive an adjusting toolrearwardly insertable from the exterior of the applicator for axialadjustment of the inner member relative to theouter member withoutrequiring system shutdown.. Either the outer lip or both the outerand'the inner lip may be tapered a few degrees, as shown, to permit ofchanging the gap spacing and the thickness of the liquid film suppliedto the forward edge of the applicator by axial adjustment of the innermember relative to the outer member. By oppositely inclining or taperingthe curved surfaces of the outer and inner members forming therearwardly diverging paint passage 32, the width of the dischargeorifice and, therefore, the paint flow may be increased by axialmovement of the inner member in either the forward or rearwarddirection. Viewed as a nozzle, this construction may aid in shaping thespray pattern from the nozzle by reason of the different spray coneangles that can be obtained therefrom.

In order to reduce corona loss and electrical leakage, all corners and.edges of the applicator structure's described herein should be roundedexcept for their attenuated forward discharge edges which are ofcontinuous extent transversely of the axis of the applicator. A

In operation, the applicator 10 is connected by a conbeen found tooperate best when the paint is fed from the top when its axis ishorizontal, so that the pressure difference in the annular passage 32due to gravity head is counteracted by the pressure difference thereindue to flow friction and turbulence.

With a potential difference of approximately 190 kilovolts or upwardsbetween the grounded workpieces and the applicator, the thin liquid filmsupplied from the internal paint annulus to the forward edge of theapplicator will become charged with electricity and will be caused bycataphoric action to flow from the ischarge edge in the form of anexceedingly line and dispersed liquid spray. The atomized sprayparticles will be charged to the potential polarity .of the electrifiedapplicator and will be ,electrostatically attracted to and deposited onthe oppositely charged workpiece. The

' atomization appears to take place from the terminus of the paintfilmat the forward edge .of the applicator where there is formed a nondisruptilvle, convective corona discharge or electric wind which isbelieved to cause the initial disintegration or rupture of the thin filminto finely divided, charged particles.

In order to reduce the weight of the applicator and electrical leakagetherefrom, either the outer member or inner member or both of thesemembers may be .constructed of electrically non-conductive material,instead of from metal. The corona discharge necessary for atomization ofthe paint film can be'obtained from either of the knife-edged outer orinner members, from both of these members, or from the exposed terminusor edge of-the paint film itself. 7

To sharp circular discharge edges of the outer and inner members willinduce the formation of cylindrical corona curtains which bound and mayunduly tend to confine the spray from the atomizer where the outer andinner members are constructed of metal. Therefore, some improvement inthe uniformity and spread of the annular spray pattern produced by theapplicator may be obtained by constructing the inner member, at least,of electrically non-conductive material, thereby eliminating or reducingthe intense corona discharge otherwise produced from the discharge edgeof a metallic member. Since it may be desired occasionally to clean orflush the applicator with paint thinners or solvents, such parts of theapplicator that may be formed of plastic should be formed of solventresisting as ,well as of paint resisting materials. 7

The applicator devices of 'Figs. 1 and 1A also may be provided with anair born or manifold 52 surrounding and suitably attached to the outermember, as shown. Air or other gas may be supplied under pressure from aline 54 to .an air annulus 6 communicating with the i 'inner end of anannular air passage 58. Air from the outer end of the passage issupplied in an annular air sheath, which surrounds the .spray from theapplicator and influences the pattern and the direction of the paint fogtherefrom.

Fig. 2 illustrates a modification for the construction of the innermember 12, which maybe made of metal or of some flexible or expandiblepaint resisting material. The forward peripheral portion of theinnermember may be'helically grooved or threaded or provided withforwardlyinclined serrations as shown at 60 for promoting I uniformpaint flow whenthe inner member is rotated or oscillated about its axisor reciprocatedaxially of the structure by rotary, vibratory or othermeans.

..ma ne .in wh e rh inne mem 9 th ap l ernf may b ctat di er e amp e'isspwn in .i is- 1A- The s em 2'2 .e t .in memh 'm v b ormed oftwosections, including an integr 1. portion 22a, i hel is rotatable -withtheinner member, and a statitonary threaded portion,22b, which is-;threadably ret e ed nih readed axial bodyopening :24. Suitablecoupling means, -such asa split or flexible bearing62, "formed 'of nylonor other material, is provided to permit rotary movement of the innermember and axial adjustment thereof by adjustrnent of the stern portion22b which fixes the axial position of the inner member. The inner membermay have a ring gear formed internally thereof as shown at 64 meshingwith a smaller drive pinion 66 secured to a drive shaft 63. Shaft 68extends through an opening in the outer body member and may be rotatedmanually for occasional rotary adjustment. The shaft 68 could be drivencontinuously by either an air or electric drive motor, or it could beoscillatably indexed by the actuating mechanism of Figs; 5 and 8 to bedescribed herein. Where the atomizing gap and the axial position of theinner member with respect to the outer member are fixed, a simplecentral drive can be employed.

Figs. 4 to 8 illustrate another form of applicator in accordance withthe present invention in which the outer and inner members 71 and 72 areshown in Fig. 5 as a p f s x a ly ne ed, shal ew swamped me a elementseach having a substantially circular lip 74 and 76, respectively, ofapproximately knife edge sharpness. The inner member is keyed to a shaft.78 that passes centrally through an axially extending stem or bossportion 8%, which is formed on the outer member and provides a bearingfor the shaft. Keyed to the shaft and adjacent the boss portion 8t) is arocker arm or lever 82, which is associated with an actuating mechanism,such as an air cylinder assembly 84, mounted on the back face of theouter member. The adjacent transverse faces of the outer and innermembers are relieved as shown at 86 and are spaced apart axially by anOilite type or other suitable thrust bearing 88 which provides a bearingsurface between the faces of the two members.

A rounded jam nut 96 and a washer 92 are provided at the end ,of theshaft adjacent the inner member, and a spring94 coaxial with the shaftis provided between the lever 82 and a washer 96, .which is retained onthe other end of the shaft by a cotter pin 98, to retain the outer andinner members in proper axial relation to each other. Screws, such as100, may be provided in the inner member so as; to back the latter offfrom the outer member during disassembly of theldevice. A standardlubricator fitting 102 is threadably received in an opening in the backface of the outer member to supply lubricant to the shaft '78 through aninclined passage 104 and annular groove 106, as shown.

The outer member 71 may be provided with a rounded sheet metal cap orcover .110, which is suitably affixed thereto, as by flat head machinescrews 112, and has a rod or handle 114 rearwardly projecting therefromby means of which the applicator device may be mounted on an insulatedsupport stand orfixture or through an insulating member to the supportstand and connected to the power supply. The conductor rod 114 isfastened to the cover by a nut 116 and a dished washer 118 and isprovided with asocket-like opening 12010 receive the high voltageconductor 44 from the power supply. The paint supply line 35 is shownextending through the cover 110 and is connected to the 'paint inletside of an airoperated paint shut-01f valve 121 whose pain t outlet sideis threadably received in a threaded opening in the back face of theouter member; An airline 122 is shown connected to the operatingairinlet of the shut-off valve.

The shut-olf valve 121 is shown in Fig. 5A as having a .paint annulusshown formedbetween the opposed curved surfacesoftheouter andinnermembers. From the annulus 1 34, the paint is supplied through theannular passage 132 to the annular orifice 134-forrned-between theextended, knife-like discharge edges of the outer and lnner members. Aremovable drain plug 136, which is threadably received in a threadedradial opening 138 and commumcates with the paint annulus 134, may beprovided to facilitate draining of the annulus during system shutdown.Another opening 140 extending between the faces of the inner member maybe provided to drain any paint that may leak between the adjacent facesof the outer and inner members.

The appliczaor devices of Figs. 4 and 4A feature the use of a novelcleaning arrangement that effectively removes trapped paint, dirt andother particles that may clog the annular paint passage and dischargeorifice and mterfere with the paint flow and spray pattern therefrom.{\s shown in the embodiment of Fig. 4, the outer and mner members areprovided with a number of uniformly spaced, narrow wiper elements 146,148 which wipe the walls of the annular paint passage 132 when the innermember 72 is oscillatably indexed and rotated. The wipers may be carbideor other metal inserts, which are pressed and cemented into uniformlyspaced slots in the paint film carrying surfaces of the outer and innermembers. They also could be formed as integral risers by selectivelyplating selected portions of the opposed curved surfaces of the outerand inner members. manner of attaching or forming the metal wipers maybe equally satisfactory.

As indicated in Fig. 7, the wipers extend from the paint annulus 130 tothe discharge edges of the inner and outer members and across theannular passage 132 between the lips of the outer and inner members.After installation in the outer and inner members, the wipers are groundto conform to the attenuated and curved lip contours of the outer andinner members, and their wiping surfaces are honed sufliciently topermit movement of the inner member with respect to the outer member. Inorder to provide complete Wiping action of substantially the entireannular paint passage, the inner member is rotatably indexed an amountapproximately equal to the arcuate distance between adjacent wipers ofthe inner or outer member.

The air cylinder actuating mechanism 84, by means of which the innermember may be oscillated relative to the outer member, includes acylinder body portion 152, which is securely mounted on the back face ofthe outer member, and an internal piston 154, which is loosely coupledto the end of one arm of the rock lever 82 by a link pin 156, as shown.An air line 150 connected to the cylinder body is adapted to supplycompressed air from a suitable air source 162 to actuate the air piston.The piston displaces the lever 82, which is connected with the innermember to the dotted position shown in Fig. 8. The lever is displacedagainst a button stop 166, which prevents damage to the wipers and ismounted on the back face of the outer member. The lever is returnedagainst another button stop 168 by a spring 170 that is connected to thelever 82 and a post 172 on the back of the outer member. In lieu of thereturn spring, the cylinder may be adapted to have air selectivelyadmitted to either side of a double-ended piston to obtain the forwardand return strokes thereof.

The inner member of the applicator need be only intermittently indexed.In operation it has been found suflicient to index the inner member butonce over intervals of from 3 to 20 minutes, but this may vary dependingupon the type of paint employed and the job. Since paint in the annularpassage 132 maybe ejected therefrom in a stream when the inner member isrotatably indexed, the inner member is indexed preferably only when theapplicator is between parts on the conveyor.

A suitable control installation, which permits the applicator to beindexed between parts on a conveyor and after a predetermined number ofparts have passed the applicator, is shown in Fig. 9. The installationincludes a conventional counter or timer device 184 that is adapted toclose a set of normally-open contacts 186 after a. pre- Any otherdetermined time or after a predeterminednuuiber of parts 46 have beenconveyed past the applicator 10. The contacts 186 are connected inseries in the energizing circuit of a conventional solenoid valve shownat 188, together with an additional set of normally-open contacts 190 ofa photo-electrically operated relay 192. The relay 192 forms a part of aphoto-electric control system which includes a lamp 194 that is locatedon one side of the conveyor 50 anda light sensitive cell 196, which islocated on the other side thereof. The cell 196 may be a selenium cellor other photo-electric device andis connected in controlling relationwith an amplifier 198 that includes the relay 192. The lamp and cell areso located relative to the applicator that when the latter is betweenparts on the conveyor, the lamp, and cell also'will be located between apair of adjacent parts on the conveyor.

The energizing circuits for the solenoid valve 188, the lamp 194, andphoto-electric system together with the input circuit of the highvoltage power supply 45 are connected for energization through a masterswitch 20.0 from local supply mains 202, 204. With the switch 200closed, the counter or timer 184 will close its contacts 186 after apredetermined time or after a predetermined number of parts have beenconveyed past the applicator. The solenoid valve, however, will not beenergized to permit compressed air to be supplied from the air source162 of the air motor until the applicator is located between parts onthe conveyor. The light beam from the lamp will then impinge upon thephotocell and cause the relay amplifier to close the contacts 190 andcomplete the energizing circuit for the solenoid valve. I

The above-described photo-electric system may be employed with anothersolenoid valve 208 to operate the paint valve 121, as shown in Fig. 5A,so that paint is supplied to the-applicator only while a part is in thespraying region, thereby preventing loss of paint when the applicator isbetween adjacent parts on the conveyor. The solenoid valve 208 suppliescompressed air from the air source 162 to line 122 to the paint valvewhen the contacts 186 of the photo-electric control system close tocomplete the energizing circuit of this solenoid. The

paint shut-off valve 121 is located preferably within the applicator, asshown in Fig. 5, and as close to the paint annulus therein so that therewill be a minimum volume of paint in the applicator gun when the paintsupply is shut off. By indexing the wiping mechanism of the applicatoreach time the applicator is between parts, a single solenoid valve andphotocell control system can be employed to operate both the indexingair motor and the paint shut-off valve.

The DC. power supply 45 may be either of the high voltagetransformer-rectifier variety or of the RF. oscillator-rectifier varietyand should be able to supply voltages up to and, in some cases, inexcess of 150 kilovolts. In the spraying of heavy pigmented material,such as may be used for the prime coating of automobile bodies, forexample, satisfactory operation may be obtained with a spacing of around18 inches between the applicator and the articles, an atomizing gap ofaround 0.004 inch and a potential difierence of from to kv. between theapplicator and the articles on the grounded conveyor. Satisfactoryatomization has been obtained with various paint compositions employedin the applicators described herein with atomizing gaps between thelimits of 0.0017 and 0.006 inch. The degree of atomization has beenfound to vary with the articleapplicator spacing, the atomizing gapspacing, the composition and viscosity of the liquid coating materialand the applied voltage, all of which variables need to be taken intoaccount in any particular installation. The paint is supplied to the topof the atomizer in sufiicient quantity and at a uniform delivery rate toreplenish the paint atomized from the edge of the applicator.

The above described applicator devices will produce an annular spray anddeposition pattern upon the surface of an article intercepting the pathof the annular spray. The outer portionso'fthe band of coating materialwhich is produced as theart'icle is moved past the applicator will havea thicker deposit of coating material than portions intermediate theends of the band. To aid inthe promotion of a more uniform coatingthickness, the applicator of Fig. 4 may be slightly modified, as shownin Fig. 4A, to include a pair of enlarged, diametrically opposed wiperelements 146a in the outer member 71 and a corresponding pair ofenlarged wipers 148a in the inner member 72 of the applicator assembly.The elements 146a, 148a are shown located immediately adjacent anddisposed on opposite sides of the vertical center line of theapplicator. Each of the wide elements replaces an adjacent pair ofnarrow wipers carried by the individual outerand inner members and is ofthe same width or arcuate length as'the arcuate distance spanned by apair of adjacent narrow wipers 146and 148 in the outer or inner members.Conceivably, the narrow wipers 146, 148 between the "wideset'sof wipersat the top and bottomof the applicator could be eliminated and the widewipers made to wipe the unobstructed portions of the gap or passage 132.

The wipers 146a and 148a will obstruct the top and bottom portions ofthe discharge orifice so that the spray and deposition pattern producedby the applicator on a stationary workpiece will be a pair of slightlycurved, spaced or separated bands elongated in a generally verticaldirection. Such an arrangement eliminates the curved top and bottomportions ofthe annular deposition pattern that otherwise would beobtained with an uninterrupted or substantially continuous annular spraypattern. A more uniform thickness of deposited coating material willthus be obtained when "the vertically disposed workpiece is moved pastthe applicator in a horizontal direction, as in Fig. 9. If thevertically disposed workpiece were moved in a vertical direction, thewide wipers should be adjacent the horizontal center line of theapplicator. With respect to the direction of movement of the plane ofthe workpiece, the wipers 146a, 148a should be arranged so that thedirection of elongation of the spaced bands produced by the applicatorwill be normal to the direction of movement of'the plane of theworkpiece so that the workpiece will intercept first one band and thenthe other and will be successively sprayed thereby.

Fig. 3 is a diagrammatic illustration of arelated form of electrostaticatomizer in which the novel wiping and cleaning feature'of the presentinvention may be included. The applicator comprises a pair of flat,circular disk elements including an upper disk element 211 and lowerdisk element 212, each'of which has an extended, attenuated dischargeedge 213, 214 which may be of knife-edge sharpness. The outer disk 211is provided with a shaft 216 which is coaxially received in a hollowshaft 218 of the inner member. The adjacent faces of the upper and lowermember may be relieved from the edge of the disks to a point inwardlythereof to form a paint supply passage 220 which extends continuouslyaround thedisks. Paint is supplied to the passage 220 through a suitableopening 222 in the lower member and flows from the passage 220 in a thinfilm to the discharge orifices 224 formed between the relieved portionsof the disks. With the atomizer spaced from and mounted with its axisparallel to the article surface to be coated, the

atomizer will produce a generally flat, 360 degree spray patterntherefrom.

' Cleaning of the passage 22 is efiected by the wipers 226 and 22$;which are carried by and maybe provided uniformly around the paintcarrying surfaces of the upper and, lower members in the mannersuggested herein. The upper member may be -o'scillatably indexed withrespect to the lower member by mechanism similar to that alreadydescribed, such as an air cylinder 230 the pistonr od 232 of'which maybe loosely coupled to a lever element 234. The element 234 is shownconnected to the shaft 216 and entends through an elongated, transverseslot inthe hollow shaft 218 of the lower member substantially as sl own.7 I

As in the case of the embodiment of Fig. 4A, one or morepairsof-enlarged wiper elements can be employed in the applicator ofFig. 3 to obstruct any portion of the circular discharge orifice andthereby interrupt any desired portion of the flat, 360 degree spraypattern otherwise obtained therefrom.

It is apparent that the novel cleaning and wiping arrangements describedherein can be embodied in various other forms and shapes ofelectrostatic atomizing applicator devices having a fine dischargeorifice and that various arrangements and forms of movable wipers in theextended passage conveying liquid to the discharge orifice can 'beemployed, all within the province of the present invention.

What is claimed is:

1. An electrostatic coating system comprising in combination a conveyorfor conveying a succession of articles to be coated into a coating zone,an atomizer in said zone spaced from said articles on said conveyor andcomprising a pair of coaxially nested members defining an annularpassage therebetween and including an outer member and an inner member,each having an attenuated forward discharge edge, fluid supply meansextending through one of said members and communicating with saidannular passage, said fluid supply means being adapted to supply liquidmaterial in a thin film to the forward discharge edge of the atomizerfor electrostatic atomization therefrom, the opposed surfaces of theouter and inner members forming the opposite walls of said annularpassage, a plurality of rigid wipers mounted in spaced relationship onsaid opposed surface of each of said outer and inner members,'saidwipers being spaced around said annular passage adjacent said forwarddischarge edge, and each wiper being mounted on one of said walls andprojecting across said annular passage into wiping engagement with theopposite wall 'of said annular passage to provide a wiping action whenone of v said outer and inner members is rotatably displaced relative tothe other member, the wipers on the inner member being equally spacedfrom each other and the wipers on the outer member being equally spacedfrom each other and angularly displaced from the wipers on the innermember, actuating means on the atomizer for moving one of said outer andinner members relative to the other, and control means operable whensaid atomizer is located between articles on said conveyor to energizesaid actuating means for relative movement of said members onlywhen theatomizer is between articles on the conveyor.

2. An electrostatic atomizer device of the character described,comprising a pair of coaitially nested members defining an annularpassage therebetween and including an outer member and an inner member,each having an attenuated forward discharge edge, the edges-being spacedfrom each other and defining the forward edge" of said annular passage,fluid supply means extending through one of said members andcommunicating with said annular passage, said fluid supply means beingadapted to supply liquid material in a thin film to the forwarddischarge edge of the atomizer for electrostatic atomization therefrom,the opposed surfaces of the outer and inner members forming'the oppositewalls of said annular passage, and a plurality of rigid wipers mountedin spaced and inner members is rotatably displaced relative to the othermember.

3. Apparatus of the character claimed in claim 2, wherein the wipers onthe inner member are equally spaced from each other and the wipers onthe outer member are equally spaced from each other and are angularlydisplaced from the wipers on the inner member.

4. An electrostatic atomizer device comprising a pair of coaxiallynested members defining an annular passage therebetween and including anouter member and an inner member, each member having an attenuatedforward discharge edge, the inner member being in sliding engagementthroughout a substantial portion of its length with the outer member,the outer wall of said annular passage provided by said outer memberbeing slightly inclined to the inner wall thereof provided by said innermember to permit of changing the width of said passage, fluid supplymeans extending through one of said members and communicating with saidannular passage for supplying liquid material as a thin film to theforward edge of the atomizer for electrostatic atomization therefrom,means for adjusting the inner member axially with reference to the outermember, said outer member having an opening therein located behind saidannular pas-. sage through which an adjusting tool may be inserted toengage and displace the inner member axially of the outer member andchange the thickness of the film of liquid supplied to the forward edgeof the atomizer, and means for rotating the inner member with referenceto the outer member.

5. An electrostatic atomizer device comprising a pair of coaxiallynested members defining an annular passage therebetween and including anouter member and an inner member, each member having an attenuatedforward discharge edge, the inner member being in sliding engagementthroughout a substantial portion of its length with the outer member,the outer wall of said annular passage provided by said outer memberbeing slightly inclined to the inner wall thereof provided by said inner member to permit of changing the width of said passage so that thepassage is most restricted when the forward edges of said members lie ina common plane, fluid supply means extending through one of said membersand communicating with said annular passage for supplying liquidmaterial as a thin film to the forward edge of the atomizer forelectrostatic atomization therefrom, means for adjusting the innermember axially with reference to the outer member, said outer memberhaving an opening therein located behind said annular passage throughwhich an adjusting tool may be inserted to engage and displace the innermember axially of the outer member and change the thickness of the filmof liquid supplied to the forward edge of the atomizer, and means forrotating the inner member with reference to the outer member.

6. An electrostatic atomizer device comprising a pair of coaxiallynested members formed of dielectric material defining an annular passagetherebetween and including an outer member of approximate sphericalconfiguration and an inner member each having an attenuated forwarddischarge edge, the inner member being in sliding engagement throughouta substantial portion of its length with the outer member, the outerwall of said annular passage provided by said outer member beingslightly inclined to the inner wall thereof provided by said innermember to permit of changing the width of said passage so that thepassage is most restricted when the forward edges of said members lie ina common plane, and fluid supply means extending through one of saidmembers and communicating with said annular passage near said dischargeedges for supplying liquid material as a thin film to the forward edgeof the atomizer for electrostatic atomization therefrom, said outermember having a rearwardly facing opening therein located behind saidannular passage through which an adjusting tool may be inserted toengage and displace the inner member axially of the outer member andchange the film thickness of the liquid supplied to the forward edge ofthe atomizer.

7. An electrostatic atomizer device comprising a pair of coaxiallynested members defining an annular passage therebetween and including anouter member and an inner member each having an attenuated forwarddischarge edge, the outer wall of said annular passage provided by saidouter member being slightly inclined to the inner wall thereof providedby said inner member to permit of changing the width of said passage sothat the passage is most restricted when the forward edges of saidmembers lie in a common plane, and fluid supply means extending throughone of said members and communicating with said annular passage forsupplying liquid material as a thin film to the forward edge of theatomizer for electrostatic atomization therefrom, said outer memberhaving an opening therein located behind said annular passage throughwhich an adjusting tool may be inserted to engage and displace the innermember axially of the outer member and change thefilm thickness of theliquid supplied to the forward edge of the atomizer.

8. An electrostatic atomizer device of the character describedcomprising a pair of coaxially nested members defining an annularpassage therebetween including an outer member and an inner member eachhaving a forward discharge edge of approximately knife-edge sharpness,said outer member having a cylindrical cavity therein coaxiallyreceiving said inner member, and fluid supply means extending throughone of said members and communicating with said annular passage forsupplying liquid material to the forward edge of the atomizer forelectrostatic atomization therefrom, said inner member being movableaxially of said outer member, the walls of the annular passage definedby said members being oppositely inclined and diverging rearwardly fromthe forward edge of said atomizer to permit of increasing fluid flow andchanging the cone angle of the spray produced therefrom upon axialadjustment of the inner member in either direction from the outermember.

References Cited in the file of this patent UNITED STATES PATENTS442,865 Kinder Dec. 16, 1890 1,832,096 Chaflee et al. Nov. 17, 19311,861,475 Hopkins et al. June 7, 1932 2,283,768 Schueler May 19, 19422,536,946 Larson Jan. 2, 1951 2,728,606 Smart et al Dec. 27, 19552,759,763 Juvinall Aug. 21, 1956 2,803,496 Ransburg Aug. 20, 1957FOREIGN PATENTS 710,852 Great Britain June 23, 1954

